not a really big deal for me, but worth mentioning: In a project I had several layers (Video (.MOV) and .PNG with alpha information, parts of them with a moving freehand-mask) in one Composite Shot and when adding the "smoke" preset, after tweaking and moving it a little, all other layers (except for the smoke) suddenly disappeared in the 3D layer window (having "View 2" switched on), whereas the Main Camera view stayed the (correct) same. The problem could be cured by saving, closing and reopening the project (without closing HitFilm as such).
General info: HitFilm Ultimate (latest update), 64 bit, Intel i5 - 750, 8 GB RAM, Geforce GTS 450. Graphics card driver a bit older from 2010 (had not updated because of the OpenGL-Problem, but as this seems to be fixed now, I am probably going to update soon, if there is an update available).
I am not exactly able to reproduce the bug "at will" or send in the project with the problem actually occurring, because saving and reloading the project (which had not changed) fixed it. So all I can say is that it happened twice, after inserting the "smoke" effect and playing around with it a little.